In the manufacture of motor vehicles, haulage vehicles and in machine construction, cavities are formed in the assembly of the vehicle or machine parts. In self-supporting bodies in particular, there are many of these cavity structures for establishing the necessary stiffness or strength of the body, including for example the so-called A, B and C pillars, sills and roof frames of automobiles and commercial vehicles. Under normal driving conditions, troublesome noise and sounds are transmitted through these cavities or are formed therein by vibrating columns of air. In order to damp this troublesome noise, the cavities are at least partly filled with sealants. These filling compounds damp or absorb troublesome noise and vibration and, in addition, prevent the entry of moisture and foreign substances.
Numerous proposals have already been put forward with a view to solving the problem of sealing these cavities to protect them against the entry of moisture and foreign substances and to reduce noise (airborne sound). These proposals may roughly be divided into four groups:
Preformed expanding materials: EP-A-453777 proposes, for example, a mechanical plug of thermally expanding sealing material to be fixed in the cavity; particulars of its composition are not provided.
EP-A-383498 describes preformed foamable parts consisting of copolymers of ethylene with ethyl acrylate which contain blowing agents. The sealing elements are preformed by extrusion and have to be fixed in the cavity to be sealed with mechanical fastenings before foaming.
Similarly, preformed thermally expanding sealing compositions based on metal salts of carboxylated ethylene copolymers (ionomers), blowing agents and tackifiers can be produced in accordance with EP-A-611778.
Preformed and cut, soft-elastic foams based on rubbers or poly-urethanes; examples of such foams can be found in DE-C-3326030, in DE-C-3516194 or in JP-A-89166939.
Foamable reactive liquid polymers such as, for example, polyurethane systems: according to JP-A-86116509, a two-component polyurethane system is directly injected into the corresponding cavities in situ by means of a mixing and metering unit, subsequently foaming and curing in the cavities. According to JP-A-93192937, the cavities may contain bag-like containers at the places to be sealed. A foaming liquid is injected into these bag-like containers which it then fills by foaming so that a section of the cavity is sealed. JP-A-91269080 describes a hot-melting composition based on thermoplastic rubbers, tackifiers and waxes or oils which are physically foamed and then cast into the cavities to be filled where they solidify by cooling.
According to JP-A-93059345, paste-like thermally expanding filling compositions based on liquid rubbers, solid rubbers, vulcanizing agents, plasticizers and blowing agents are introduced into the cavities to be sealed where they foam and vulcanize on heating. These foamed vulcanizates have very limited hardness (Shore A hardness generally below 5) and a tensile shear strength of generally well below 0.1 MPa.
One feature common to all hitherto known cavity sealing materials, also known as pillar fillers, is that they perform the sealing function and the noise-damping function (damping of airborne sound) fairly satisfactorily. In vehicle construction, more especially in automobile construction, every effort is made to make the passenger compartments stiffer to increase passenger safety without at the same time adding significantly to the overall weight of the vehicle body. Accordingly, it would be desirable if the cavity structures of the vehicles could contribute towards increased stiffness.